package com.vislardo.app.notebook.utils;

public class SnowFlakeHandler {

    // 起始的时间戳（2023-01-01）
    private final static long START_TIMESTAMP = 1672531200000L;

    // 每一部分占用的位数
    private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
    private final static long MACHINE_BIT = 5;   // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5;// 数据中心占用的位数

    // 每一部分的最大值
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);

    // 每一部分向左的位移
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  // 数据中心
    private long machineId;     // 机器标识
    private long sequence = 0L; // 序列号
    private long lastTimestamp = -1L; // 上一次时间戳


    public SnowFlakeHandler(long datacenterId, long machineId) {
            if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
                throw new IllegalArgumentException("Datacenter ID can't be greater than " + MAX_DATACENTER_NUM + " or less than 0");
            }
            if (machineId > MAX_MACHINE_NUM || machineId < 0) {
                throw new IllegalArgumentException("Machine ID can't be greater than " + MAX_MACHINE_NUM + " or less than 0");
            }
            this.datacenterId = datacenterId;
            this.machineId = machineId;
    }



    // 生成下一个ID
    public synchronized long nextId() {
        long currentTimestamp = getCurrentTimestamp();
        //简单处理时钟回拨问题
        if (currentTimestamp < lastTimestamp) {
            long offset = lastTimestamp - currentTimestamp;
            if (offset <= 1000) { // 如果回拨时间小于等于1s，等待
                try {
                    Thread.sleep(offset);
                    currentTimestamp = getCurrentTimestamp();
                    if (currentTimestamp < lastTimestamp) {
                        throw new RuntimeException("等待后仍存在时钟回拨问题，无法生成ID");
                    }
                } catch (InterruptedException e) {
                    throw new RuntimeException("等待时线程被中断", e);
                }
            } else {
                // 如果回拨时间过长，直接抛出异常
                throw new RuntimeException("存在时钟回拨问题，无法生成ID");
            }
        }

        if (currentTimestamp == lastTimestamp) {
            // 相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                // 同一毫秒的序列号已经用完，等待下一毫秒
                currentTimestamp = getNextTimestamp(lastTimestamp);
            }
        } else {
            // 不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastTimestamp = currentTimestamp;

        // 时间戳部分 | 数据中心部分 | 机器标识部分 | 序列号部分
        return ((currentTimestamp - START_TIMESTAMP) << TIMESTAMP_LEFT)
                | (datacenterId << DATACENTER_LEFT)
                | (machineId << MACHINE_LEFT)
                | sequence;
    }

        // 获取当前时间戳
        private long getCurrentTimestamp() {
            return System.currentTimeMillis();
        }

        // 获取下一个时间戳
        private long getNextTimestamp(long lastTimestamp) {
            long currentTimestamp = getCurrentTimestamp();
            while (currentTimestamp <= lastTimestamp) {
                currentTimestamp = getCurrentTimestamp();
            }
            return currentTimestamp;
        }

}


